1.   This can happen with sexually transmitted diseases only if the average infected person infects more than one other person.

2.   Once a person is infected they may recover naturally or they may become a chronic carrier of the virus.

3.   Although the precise number of anthrax spores required to infect a person is uncertain, any debate over numbers in the thousands is somewhat academic.

4.   But once a person is infected, no amount of hair dressing will work.

5.   Genotypic tests genetically map part of the particular strain of HIV infecting a person and look for key mutations believed to correlate to resistance against specific drugs.

6.   However, that type of vaccine always carries with it the risk of infecting the person it is supposed to be protecting, he said.

7.   If antibodies are present, the person is infected.

8.   If such a person is infected with a pathogen, it can easily spread to others.

9.   It is generally believed that once a person is infected with HIV, the virus that causes AIDS, that they are infected forever.

10.   It takes on average about a decade from the time a person is infected with HIV until he or she develops AIDS.